The well publicized advances in integrated circuit technology have rendered these electronic components increasingly small. Among many technical difficulties to be solved in connection with the miniaturization of these components is the connection of wires thereto. Clearly it would be of little avail to make a miniature circuit if the wires could not be connected to it due to operator inability to physically connect the wires to the very small contact spaces provided. Accordingly, there have been developed a class of bonding machines, referred to herein as host machines, in which once an operator has precisely located the integrated circuit chip or "die" with respect to a reference location, the host machine then is fully capable of attaching the bond wires to bonding pads at predetermined locations with respect to the reference location, e.g., by application of ultrasonic or heat energy. The pattern recognition system of the invention is described in connection with precise location of an integrated circuit die with respect to a host wire bonding machine but has utility in location of other workpieces with respect to other sorts of corresponding hosts.
Presently, the location of the die with respect to the reference location is either done by an operator or by automated machinery. Clearly it would be desirable to replace the operator with automated machinery so that labor could be saved. However, the automated machinery available to date has not been adequate to satisfy the needs of the art.
Typically dies are supplied pre attached to the remainder of the integrated circuit of which they are the main component. The body of the integrated circuit itself can be accurately located with respect to the bonding machine. However, the precise location of the die on the body of the eventual integrated circuit device may vary from its nominal position by on the order of 10 mils in any direction and may additionally be angularly displaced from its proper orientation. The manufacturing capabilities of present day integrated circuit operations are such that it is important to be able to properly bond leads to integrated circuit chips displaced angularly on the order of .+-.7.degree., and linearly by up to 10 mils in any direction from the nominal position. It will be appreciated by those skilled in the art that the bonding pads to which the wires must be attached are typically only about 4 mils square. Accordingly, to locate these bonding pads with sufficient speed and accuracy to enable proper and rapid bonding is a task of technical complexity and one which has not been adequately performed in the prior art.
Prior art pattern recognition systems are typically of the template matching kind, in which a stored portion of the pattern to be located is compared iteratively with various corresponding portions of the "target" pattern to be precisely located. See, e.g., U.S. Pat. No. 4,200,861 to Hubach et al. This, it will be recognized, is a very time consuming procedure, particularly where the target may be angularly displaced, as the relative movement of the stored portion required with respect to the target must be simultaneously made in both X and Y directions--that is, X and Y displacement cannot be determined independently by a template matching system, as both must be found simultaneously for a match to be detected.